The long-term objective of this study is to gain insight into the regulation of lipoprotein lipase (LPL) and its potential role in the pathogenesis of atherosclerosis. We propose that LPL, together with cell surface lipoprotein receptors and apolipoprotein ligands, plays a crucial role in this process. We suggest that the action of LPL on triglyceride- rich lipoprotein particles promotes their uptake by arterial smooth muscle cells (SMC) and macrophages and accelerates foam cell formation. LPL is synthesized by adipocytes, myocytes and macrophages and is mainly deposited on the endothelial surface of blood vessels. Developmental, hormonal and cell type-specific control of LPL expression will be the focus of this proposal. A major effort will be directed at identification of cis-acting elements responsible for regulation of LPL gene expression in both macrophages and SMC. Both in vitro and in vivo approaches are designed to explore these regulatory elements. The in vitro experiments are aimed at identifying potential regulatory sequences (both negative and positive) by virtue of their ability to bind specific transcription factors (as revealed by nuclease hypersensitivity, genomic footprinting and gel mobility retardation assays), and to modulate expression of a heterologous reporter gene in transiently transfected macrophages and SMC in culture. DNA constructs will be used to investigate regulatory sequences responsible for lineage-specific and developmental stage-dependent expression in transgenic mice. This latter approach is extremely valuable and necessary for the following reasons. First, it allows very rapid assessment of expression (using lac Z as a reporter gene) in a variety of tissues during different stages of development. Second, it provides an in vivo system to verify results of in vitro experiments. Third, it provides a model with which we would able to test the hypothesis that overproduction of LPL accelerates foam cell formation and atherosclerosis. Another aim of this proposal is to determine the relative contribution of LPL from SMC and macrophages in the arterial wall at different stages of development and also at different stages during atherogenesis. In situ hybridization with RNA probes and immunocytochemical techniques will be employed. We have chosen to study LPL both because of its possible role in modification of lipoproteins within the plaque, and because differential cell type expression of this gene by the key cells of the lesion may provide clues as to the general properties that distinguish these cell types from others and control each cell's unique contribution to the lesion.